Vitamin B2 - Riboflavin

Question 1

List dietary sources of riboflavin

Answer 1

Milk and milk products
Eggs, meat, legumes
Green leafy vegetables
Fruits
Cereal grains

Question 2

Describe the digestion of riboflavin

Answer 2

Only free riboflavin can be absorbed
Animal sources
- bound noncovalently to proteins
- freed by action of HCL or proteases
Plant sources
- in the form of FAD, FMN, and riboflavin phosphate
- freed by intestinal phosphatases

Question 3

Describe the absorption of riboflavin

Answer 3

Absorption occurs primarily in the proximal small intestine
Two mechanisms
1. Active transport - saturable, energy-dependent carrier
2. Passive diffusion
Rate of absorption is proportional to the dose, to a max of 25-30mg

Question 4

Describe the transport and metabolism of riboflavin

Answer 4

Riboflavin is phosphorylated to FMN and FAD on absorption into enterocytes
FMN is then dephosphorylated back to riboflavin for transport in the blood
- albumin is the primary transport protein
Riboflavin is transported to the liver for conversion to FMN and flavin adenine dinucleotide (FAD)

Question 5

Describe the storage of riboflavin

Answer 5

Not well stored in the body

Greatest concentrations found in liver, kidney and heart

Question 6

Describe the function and mechanism of action of riboflavin

Answer 6

FMN and FAD are active functional forms
Participate in the release of energy from carbohydrates, fats and proteins
- picks up H+ ions and transports them to the ETC
Required for maintenance of mucosal, epithelial and eye tissue
Necessary for activation of other vitamins such as folate and B6
Aids B6 in the conversion of tryptophan to niacin
Coenzyme for monoamine oxidase which is required for metabolism of: dopamine, tryamine and histamine
Coenzyme for glutathione reductase which reduces the oxidized form of glutathione so we can use it again

Question 7

List interactions with other nutrients with riboflavin

Answer 7

Absorption of riboflavin is inhibited by:

• zinc
• copper
• iron
• manganese
• ETOH

Question 8

Describe the excretion of riboflavin

Answer 8

Created primarily in the urine

Question 9

Describe consequences and symptoms of deficiency of riboflavin

Answer 9

Ariboflavinosis:
Rarely occurs in isolation
No clear riboflavin deficiency disease
Clinical symptoms of deficiency:
- angular cheilosis/stomatitis, glossitis 
- seborrheic dermatitis (dandruff)
- anemia
- peripheral neuropathy, weakness
- depression

Question 10

Who has an increased Rick of developing a riboflavin deficiency?

Answer 10

Alcoholics
Elderly
Adolescents (black teenage girls)
Low income
Professional women
Strict vegans (don’t absorb as well from plant source)
Homozygous mutation in methylene tetrahydrofolate reductase have increased riboflavin requirement
Use of certain medications, such as: OCP, anticonvulsants and chlorpromazine
Calcium supplementation decreases riboflavin absorption when taken together
Diabetes, trauma and stress increase excretion of riboflavin

Question 11

Describe consequences and symptoms of toxicity of riboflavin

Answer 11

None reported and no UL

Question 12

Describe the assessment of nutrient status of riboflavin

Answer 12

Measure activity of erythrocyte glutathione reductase
- >40% increased activity with addition of FAD indicates deficiency
Serum and urinary concentrations less indicative of tissue stores

Question 13

Discuss some of the therapeutic uses (clinical indications) of riboflavin

Answer 13

Migraines as preventative, not acutely